There's an open issue[1] with people assigned to it. And even documentation for the new hobbled API that is available in both the beta and dev channels[2].
Chromium still being the better browser in most ways, I wonder what could be done about this. Maybe it's time to have a simple patchset for doing content blocking natively in the engine. With patches like that floating around, they can't very well say that it's an efficiency issue like they do in the doc describing Manifest V3.